Color television receiver with large projection screen



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V, v AMPLI ER PHASE- osrecron DELAY cmcun PHASE- DETECTOR IUVEVTO'RGama; VkLEA/sn Nov. 8, 1960 G. VALENSI I 4 2,959,635

COLOR TELEVISION RECEIVER WITH LARGE PROJECTION SCREEN Filed Oct. 14,1959 7 Sheets-Sheet 3 G. VALENSI Nov. 8, 19 60 COLOR TELEVISION RECEIVERWITH LARGE PROJECTION SCREEN Filed Oct, 14, 1959 7 Sheets-Sheet 4 mag-J6me Ms km)? Nov. ,8, 1950 G. VALENSI 2,959,635

COLOR TELEVISION RECEIVER WITH LARGE PROJECTION SCREEN Filed Oct. 14,1959 7 Sheets-Sheet 5 MULTI- i MBRATOFS INVERTING TRIODE 413 MEDAMPLIFIERS V353 [a l i 9; INVERTING 1 TRIODE INVERTING' 'TRIODE l-JGATEDAMPLIFIER OSCILLATORS av v MIXER "GATED AMPLIFIERS AM F IER y ,p TAGEGENERATOR I Eflah ELECTRONIC 1;. SWITCH m 9,9 but SQUARE- 1 WAVE"OSCILLATORS I H GENERATOR If, I, J ban 9 suzcmomcj symcu FREQUENCYMODULATOR Fr 2f 2e NVEVTFR 6501265; vALeusl ihs AsaJT Nov. 8, 1960 I G.VALENSl 2,959,635

COLOR TELEVISION RECEIVER WITH LARGE PROJECTION SCREEN Filed Oct. 14,1959 7 Sheets-Sheet 6 5, L525, 15's I 5' [P .J I -L--.. L0

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G. VALENS! Nov. 8, 1960 COLOR TELEVISION RECEIVER wxm LARGE PROJECTIONSCREEN Filed Oct. 14, 1959 7 Sheets-Sheet 7 WI/EUTOR emxe s ant/cam-United States Patent O COLOR TELEVISION RECEIVER WITH LARGE PROJECTIONSCREEN Georges Valensi, 3 Rue des Chaudronniers, Geneva, SwitzerlandFiled Oct. '14, 1959, Ser. No. 846,411

Claims priority, application France July 16, 1959 14 Claims. (Cl.1785.4)

This invention concerns a television system in which a carrier wave(modulated by a luminance signal 1) carries the information for adetailed drawing of the scene to be shown at distance, whereas 'asubcarrier wave (modulated by a chrominance signal chr) carries theinformation for the colors of the various elements of said scene. It iswell known that the human eye requires less color information thandrawing information; therefore the chrominance spectrum occupies only arelatively small part of the frequency band occupied by the lumi-' nancespectrum; for example, the luminance occupies a band 4 megahertz wide,whereas the two side-bands of the color subcarrier (together with thesubcarrier itself) occupy only a band 1 megahertz wide.

A satisfactory reproduction in colors of the scene scanned at a distanttransmitting station can be produced by superimposing, upon a Verydetailed black and white drawing (on a projection screen), a relativelycoarse colored picture, made of a relatively small number of toucheshaving different colors. In order to secure the persistence of theimpressions on the retina, the drawing with 625 scanning lines (in theEuropean television standards) must be repeated 25 times per second;similarly, in the American television standards, the drawing, with 525scanning lines, must be repeated 30 times per second; in both cases, theaspect ratio of the picture is 4/3. Assuming a band width of 400,000hertz for one side-band of the modulated color subcarrier received atthe receiving television station, the coarse colored picture mentionedabove would contain only: in Europe distinct colored elements, and inUnited States of America:

distinct colored elements. In Europe the coarse colored picture willhave 110 lines of 146 distinct elements each; in U.S.A., it will have100 lines of 133 distinct elements each.

In the American color television standard (National Television StandardsCommittee System, in brief N.T.S.C. System), the color subcarrier isboth phase modulated and amplitude modulated; the phase gives the hue,and the amplitude givesthe degree of saturation Ice 2,959,635

Figure 1 is a schematic representation of the color television receivingstation in accordance with the invention; EP is the projection screen;in this case the received; video-signal is assumed to have the spectrumshown on";

Figure 2a.

Two projectors (TC TC of the Eidophor type areused simultaneously, eachhaving a transparent plate (PL PL rotating continuously around avertical axis (A A the upper faces of said plates being madeelectro-conductive by means of a very thin suitable transparent coating;the motions of said plates (PL PLg) are perfectly synchronous, becausethe same electricmotor (not shown on Figure 1) drives said plates'bymeans of the same mechanism (Mec). A thin layer (P P of a viscous oilhaving an appropriate electric conductivity is spread over the uppersurface of each plate (PL PL Transparent windows (f f )'permit" theillumination (through trnasparent plates PL PL of said oi-l layers bymeans of powerful sources of white light (S S located at the focus ofconcave mirrors and also at the focus of collimating lenses (LC LC sothat parallel luminous rays illuminate (at normal incidence) twohomothetic rectangles (E E of said oil '1 layers (P P these rectangles(E B are scanned respectively by the pencils of the electrons producedby' cathodes c c accelerated by anodes a a united into a cross-overinside aperture diaphragms d Lizconcentrated on the oil layer byfocussing magnetic coils sf sf horizontally deflected by coils h' h' andbyv plates h h and vertically deflected by coils V1,, v

The electroconductive faces of plates (PL PL )"in contact with oil areraised to a high positive electric: potential referred to cathodes (c cthebomb'ardinga electrons produce (on rectangles E E some"deforma-:

tions of the oil surface, due to the electrostatic forces developed bythe electron spots; but these deformationsdisappear after a fraction ofa second, because the oil is slightly electroconductive.

Rectangle E (of oil layer P in tube TC isimaged; through transparentwindow f by objective lens L0 onto projection screen EP, in order toproduce a detailed black and white drawing of the scene being scannedatw the transmitting station; rectangle E (of oil layer P in tube TC isimaged, through transparent window (f' by objective lens L0 ontoprojection screen EP,

in order to superimpose colored touches upon said,

drawing.

Like in a classical Eidophor projector for black an white television,two bar systems (B B are associated with tube TC and lens LC images barsystem-v B onto bar system B in such a manner that a luminous" ray (suchas r going through, a part of rectangle-'E 7 without deformation isstopped by bar system B whereas a luminous ray (such as r going througha part having a deformation goes freely through the slits of B ;fafter;objective lens L0, and after reflection on mirror M, said luminous ray rcontributes to the production (on screen EP) of the White image ofthercorresponding part of E the brightness of said image beingproportional to theimportance of the deformation of said part of EThere-1 fore, in a classical manner, the desired black and white drawingis produced by Eidophor projector TC on screen 0 The object of thepresent invention is the creation (by means of tube TC of the othercoarse colored image of the scene being scanned at the transmittingstation, in applying the principles illustrated by the appended Fig ures3, 3a and 3b-or 3d and Be, or 3 The diffraction of white light throughthe parts of the oil layer having a deformation producing (as explainedhereafter) not only a white luminous point, but also; colored spectra onboth sides of said'white point, it could Piten ted Nov. 8, 1960theoretically be possible to use the same Eidophor projector forproducing the drawing (under the control of the luminance signal) andthe color (under the control of the chrominance signal); but there wouldbe a risk' of interference between the respective actions of luminancesignal I and chrominance signal (chr)said interference producing eitherdisturbing colored fringes, or undesirable color errors, on projectionscreen EP. The purpose of the present invention is to separate clearlythe respective actions of luminance signal I and chrominance signal(chr).

The invention will be better understood in referring to the appendeddrawings, in which:

Figure It: represents the left part and Figure 16 the right part of thecolor television receiving station in accordance with the presentinvention;

Figure 2a shows the spectrum of the received composite video-signal V inthe N.T.S.C. System;

Figure 2b shows the circular diagram for the phase of the modulatedcolor subcarrier in the N.T.S.C. Systern;

Figure 20 represents a phase detector;

Figure 2d represents the decoding electrode of the hue decoding cathoderay tube Td of Figure 1;

Figures 22, 2 and 23 show a modification of part of Figure 1;

Figures 3, 3a, 3b, 3c, 3d, 3e and 3 illustrate the performance ofprojector TC of Figure 1, producing the coarse colored picture of thescene being scanned at the transmitting station;

Figure 4 represents the color triangle divided in sectors correspondingto the various chromaticities that the human eye can discriminate easilyfrom each other.

Figure 4a shows the saturation decoding cathode ray tube Td and the huedecoding cathode ray tube Td, in case of a color television system basedon the color triangle of Figure 4;

Figure 1c shows a single Eidophor projector TC, re placing the twoEidophor projectors (TC TC of Figure 1; and Figure 1a shows parts ofsaid single projector TC of Figure 1a. Figure 1 represents schematicallythe invention as applied to the American N.T.S.C. color televisionsystem.

Figure 3 shows the source of white light S of Figure 1, as well as thecollimating lens LC and the plate PL of tube TC with its oil layer P R RR represent elemental light diffracting gratings produced by theelectrons (issued from cathode on part E of oil layer P said gratingshaving respectively n n n parallel rippled lines per millimeter; theselines (perpendicular to the plane of Figure 3) are the so calleddeformation of the oil surface due to the pressure distributioncorresponding to the discrete linewise electrical charges distributionproduced by the electron pencil which is horizontally deflected not onlyby magnetic coil h' (energized by a sawtooth wave at the scanning linesfrequency), but also by plates I1 energized by a frequency modulatedsine-wave as explained hereafter. In the absence of said sine-wave, auniform distribution of electrons would be produced on the oil surfaceduring the linear part of the sawtooth waveform applied to coil h' andsaid oil surface would remain smooth; if, on the contrary, saidfrequency modulated sine wave is applied to plates 11 the size of theelectron spot varies from point to point on the oil surface, and adeformation, in form of an elemental diffracting grating R is produced.

RL (Figure 3) is a network of small elemental lenses (l l having all thesame focal length and corresponding to diifracting gratings R R R Thefocal points of all these elemental lenses are on the same plane F whichcontains a mask M constituted by opaque parts (m, m) separated from eachother by transparent parts (e); although mask M is exactly on focalplane F, it is n being the number of parallel lines of grating R; byunit length, because s; (or s' is a first order spectrum, and becausesource S illuminates oil layer P at normal incidence.

Figure 3a shows, for example, the luminous groups (s l s' (s l s' (s Is' corresponding to elemental diffracting gratings R R R of Figure 3.bands m and m (of mask M) cut ofl? the central images 1;, I I as well asa great part of spectra s s' s s s;,, s';; Therefore the onlymonochromatic luminous radiations produced by the difiracting gratingswhich can go through transparent parts 2 (of mask M) and reach theprojection screen EP through objective L0 (Figure 1) are those havingwave-lengths comprised in an interval AA given by the formula:

if 1, Ad and A7\ are also expressed in millimeters.

It is desired that Al corresponds to nearly one third of j the normalvisible spectrum, which extends from red light (A,=7.l0* mm.) toviolet-blue light (A =4.10- mm.).

Therefore the order of magnitude of the width e of a transparent part ofmask M (Figure 3a) should be: e=f-m- -1O" mm.

The Eidophor television projectors commonly used for black and whitetelevison have a hair-pin cathode producing an electron beam of 20microamperes under an accelcrating voltage of 20 kilovolts, and theassociated electron optics produces, on the oil layer, an electron spot0.02 millimeter wide and 0.1 millimeter long, said spot being one lineof an elemental diffraoting grating. It is desired that the distancebetween two such lines equals at least twice the width of a line, sothat the maximum number of lines per millimeter is 16. t

Figure 3b shows with more details one elemental diffracting grating R ofoil'layer P and the corresponding elemental lens 1 within the network oflenses RL of Figure 3. It is necessary that the two first order spectra(s s' produced by ditfracting grating R, reach (entirely) thecorresponding elemental lens 1 As explained hereafter, the electron beamemitted by cathode c of tube TC (Figure 1) produces, on successsivehorizontal scanning lines of rectangle E of oil layer P within the sameelemental square of E below lens I different diffracting gratings (R R Rhaving appropriate numbers of lines per millimeter (n n n,) forproducing (through the transparent parts e of mask M) blue, green andred lights respectively; as explained here after, n n n The maximumdiffraction angle (u corresponds to the red radiations (wave lengthmillimeter) diffracted by the most diffracting grating R If 1 is thewidth of elemental lens I; (Figure 3b), d the distance (in millimeters)between oil layers P of tube TC and network RL of elemental lenses, thefollowing conditon must be fulfilled for the first order spectra:

The, opaque As :04 10* mm. (blue light), A =0.5 10- mm. (green light,and A,-= 0.7 10- mm. (red light),

n -4 V 5 7 For example, if n =16, n 12.8 and n,=9.14. If n =8, n =6.4and n,=4.57. The distance between P and RL (Figure 3b) is, in both casesdetermined by the above formula when l; and n are known.

The focal length 1 of elemental lenses 1, of network RL and thedimensions of the various parts (m, m, e) of mask M (Figures 3a and 3b)must be such that objective lens L (represented by a single horizontalline on Figure 3b, and having a diameter of O millimeter) receives onlythe lights of desired colors, but also receives the colored lights ofone third (blue, green or red) of each first order spectrum diffractedby the various elemental squares of rectangle E of oil layer P (Figure1).

As the red radiations must (at most) reach the right end of theconsidered element (m, e, m, e, m) of mask M, and as this element has awidth 6 Z2 -+e+e) S being the width of an opaque part m, whereas 5-=2eis the width of an opaque part m, the following condition must besatisfied:

Objective lens L0 must cover the 13,300 elemental squares of rectangle Eof oil layer P (100 lines of 133 elemental squares each) in the case ofthe American N.T.S.C. color television system; therefore the width ofmask M must be 133 l, and its height must be 100 1.

Consequently:

O=ZV 133 100 =l /27,689= 1671 If, for example, 0:250 millimeters, then:

250 Z 1.49 milllmeters and The mask M (the dimensions of which are sodetermined) can be made by photographing a much enlarged black and whitedrawing, upon a thin grains photographic film. The width 1 of anelemental lens I, of network RL must be equal to the width l of oneelement of mask;

M; therefore l =1.49 millimeter.

Rectangle E1 of oil layer P must have the same dimensions as mask M;therefore its width is E=133l=133 1.49=198 millimeters Objective lens L0in association with the elemental lens I, of network RL, produces, onprojection screen' EP (Figure 1) a coarse colored picture of the scenebeing scanned at the distant transmitting station; if said picture has awidth of C meters, and if projection screen EF is at a distance of Dmeters from objective lens L0 (which images rectangle E onto screen EP),the magnification produced by this optical system is:

Q g E and the focal length of lens L0 must be:

If, for example C=6 meters, D=15 meters, as E -0.198

meter,

The distance between L0 and oil layer P is of the order of 60centimeters. The optical system, constituted by the elemental lenses ofnetworkRL and by objective lens L0 must be well corrected forachromaticity and for the field; but the conditions to be imposed forthe diificult optical problem for mirrors M and M of Figure 1 1;moreover, some correction can be made electircally in scanning the twohomothetic rectangles E and E (in synchronism) within tubes TC and T Crespectively.

The prototype'of lens network RL (Figure 3) is ob A number of cubic eletained in the following manner. ments (having 1.5 millimeter sides) arecut into a glass plate having parallel faces; these cubic elements arejuxtaposed on a sphere having an appropriate radius of curvature, andthey are simultaneously all shaped and polished.

Then these elemental lenses are juxtaposed on a plate covered with anappropriate paste which is later polymerised by heating, in order toobtain a solid block, which is precisely the desired prototype. as amould, a number of lens-networks such as RL (Figure 3) can be obtained(cheaply), in Plexiglas (meta chrylate of methyle).

Figure 3d shows a modification of the optical system of Figures 1 and 3.In this case, mask M is juxtaposed to network RL of elemental lenses, asFigure 3e shows it in a more detailed manner. Also a bar system M isused, having opaque parts b wide), separated by slits;

(a wide); finally, use is also made of a screen E (provided withrelatively narrow holes), located in the focal plane of the elementallenses of network RL. The purpose of using bar system M and screen E isto secure a good parallelism of the white light rays illuminating (atnormal incidence) the various elements of rectangle E of oil layer P andto cut off any stray light, other than the colored lights which it isdesired to throw on projec tion screen EP.

On Figure 3d, S is a" powerful source of White light (for example, anelectric arc in pressurized xenon),

With this prototype.

located at the center of asmall spherical mirror ms, which images saidelectric arc onto itself. S is the image of S1 through lens L, withinthe hole of diaphragm d. S' is located at the focus of collimating lensLC which illuminates (at normal incidence) rectangle E of oil layer Pthrough transparent plate PL of tube TC (Figure 1). The electronsemitted by cathode C of tube TC create elemental difi'racting gratings(such as R R above slits a of M, Figure 3e). l 1 are the elementallenses of network RL corresponding respectively to said gratings R R Theopaque parts (m, m) of mask M (separated by transparent parts e of saidmask) cover the bases of said elemental lenses l 1 as shown on Figure3e. As the center of each opaque part In of M is just above each slit 4of M, the non-diffracted white light is cut off by said part m, whereasthe colored light (diffracted by grating R for example) goes through thetransparent parts e, both sides of m; therefore, at the focus ofelemental lens 1 are produced two small colored images (S" and S" oflight source S very close to each other, inside a hole of screen E.Objective lens L (which in association with the elemental lenses of RLand with mirror M images rectangle E of oil layer P onto projectionscreen EP) produces colored touches corresponding respectively to saidelemental lenses, in such a manner that said touches build a coarsecolored picture of the scene being scanned at the distant transmittingstation.

An elemental diffracting grating R; (having n lines per millimeter)diifracts the blue light ,=0.4.10 mm.) of an angle a and difiracts thered light ()\,=0.7.l( mm.) of an angle a t sin a =n A sin a =n J Theseangles (a (1,) are small enough for having a tangent equal to the sinus.

If D designates (in millimeters) the distance between oil layer P andthe juxtaposed mask M and network of lenses RL, the (normal) first orderspectrum occupies (on mask M) the space limited by points distantrespectively of d and d, from the middle of opaque part In (or from themiddle of the base of the corresponding elemental lens 1 with:

d =D tan a =Dn -7\ (which corresponds to blue) d,=D tan eq=Dn -7\ (whichcorresponds to red) The transparent part (e) between two opaque parts(m, m) must correspond to one third of said normal first order spectrum;therefore:

@anmomillimeter In order to have, on projection screen EP, colors asmuch saturated as it is economically possible, it, should be thesmallest of the numbers n 11,, 11,, therefore 11, should be made equalto 4.57. Therefore:

e=D 4.S7 X 10* millimeters (l) The opaque part m of mask M must have awidth 6 such that the following condition is satisfied:

or 6::2D-32-10- (2) The objective-lens L0 (having a diameter 0millimeters) must cover all the elements of mask M, the width of oneelement being:

6 being the width of an opaque part In of mask M. Therefore:

If Equation 4 is subtracted from Equation 3, and if account is taken ofEquation 2, the following equation is.

obtained:

14900 D 163 millimeters 6=2 163 32 10-*: 1.04 millimeters Therefore:e=163 4.57- l0- =0.074 millimeter Again, the width of rectangle E of oillayer P of tube TC (Figure l) is 133-l=l98 millimeters, each elementalsquare of said rectangle E having sides of 1.5 millimeter.

In case of Figure 3d, the system made of network RL of elemental lensesand mask M can be realized in the following manner: in a rigid frame areassembled 133 strips (moulded in Plexiglas, metachrylate of methyle)having each elemental lenses 1.5 millimeter wide; this assembly issettled upon a mask M obtained by photographing a much enlarged blackand white drawing on a thin grains photographic plate.

In the case of Figures 3d and 3c, the focal length of objective lens L0can be 080 meter, said lens L0 being at D=25 meters of a projectionscreen G=6 meters wide; the magnification produced by said objective lenbeing the distance between network RL of elemental lenses and screen Ecan be of the order of 50 millimeters.

Figure 3 shows another modification of the optical system associatedwith tube TC, of Figure 1. In this case, no network of elemental lenses(such as RL, Figure 1) is used; but use is made of two bar systems M, M,conjugated with each other in, such a manner that the slits (a) of M arein front of the opaque parts (m) of M, whereas the opaque parts b of Mare in front of the transparent parts (e) of M. A powerful source ofwhite light S (not shown on Figure 3f) illuminates, at normal incidence,the oil layer P on which the electrons, emitted by cathode c of tube TC;(Figure 1), create elemental difiracting gratings R on each elementalsquare of a rectangle E of said oil layer P For example, R (Figure 3 1)corresponds to 3 gratings (R R R juxtaposed on parallel lines in a plane(P perpendicular to the plane of Figure 3 said gratings havingrespectively n 11,, n lines per millimeter.

Lens objective L0 (represented as a single horizontal line on Figure 3images said rectangle E onto projection screen EP, after reflection onmirror M (Figure l), and objective L0 covers entirely the 100 lines of133 elements of mask M.

Each dilfracting grating (R produces, at a distance D millimeters fromoil layer (P a central white image of source 8,, and, on both sides ofsaid image, various diffraction spectra. The first order spectra arewell separated from each other and quite distinct; the spectra of 2nd,3rd orders overlap each other and are much less brighter, so that theyproduce (on projection screen EP) only a small diffuse white light;account should be taken of that in the adjustment of rheostat r, rassociated with pentode L (luminance Weighting device) shown on Figurel, as explained hereafter.

, In the first order diffraction spectra, the red radiations are themost distant from the middle of opaque part m of mask M in front ofditfracting grating R this distance of the red radiation has thefollowing values in case of gratings R R R, respectively;

(n n,, n d d d and D being expressed in millimeters and =0.7-lOmillimeter.

If 6 is the width of an opaque part In of mask M, and if e is the Widthof a transparent part c of said mask M, an element of M has a width:

e e 54- F +8 As objective lens L (having a diameter of O millimeters)must cover all the elements of mask M (100 lines of 133 elements),

The greatest number of lines per millimeter of gratings R; (as mentionedabove) is n =l6 lines per millimeter. It is necessary that the bluethird of first order spectrum goes alone through transparent part e ofmask M in case of a dilfracting grating R -that the green third alonegoes through (e) in case of a diffracting grating R and that the redthird alone goes through (e) in case of a diifracting grating RTherefore:

Two cases can be considered:

e=D.n,.10- mm.

In the first case (n =16; n =12.8; n,=9.l4), with 0:250 mm., thefollowing values are obtained:

2X 108 16 X 4.10 1.38 millimeters e= 108 9.l4.l0 =O.0987=O.1 millimeterIn the second case: D=2l7 mm., 5:1.39 mm.,

e=0.099=0.1 mm.

Some care must be taken for focusing, in an appropriate manner, theelectrons on the oil layer during all the scanning of said layer by theelectron pencil. Figure 3c shows the rectangle E of oil layer P of tubeTC of Figure 1, and shows also a horizontal segment marked 108millimeters (RL, M having the same width as rectangle E this sega mentis the network RL of elemental lenses in caseiof Figure 3b, or Figure3d, and is the mask M in case of Figure 3f. RL, M) is, in any case, anobstacle for the electron pencil, so that the angle between the electronpencil scanning rectangle E and the oil layer must be less than 50degrees (see hereafter). cm (Figure 3c) represents one horizontalscanning line, 0 the cathode of tube TC a the anode, d the diaphragm(cross-over), h the auxiliary horizontally deflecting plates energizedby the frequency modulated wave A sin w t, sh the focussing solenoid,and h'j, v the yoke made of the horizontally deflecting coil h' and thevertically deflecting coil v (Figure 1); h' and v move the electron spot(over rectangle E with constant velocities (v: for horizontal scanning,and v for vertical scanning), while plates h; make the electron spotvibrate at the instantaneous frequency The focal length F of solenoid sf(having a winding of It turns, with a mean radius r centimeters, andthrough which flows an electric current of i amperes) is given by theformula:

F centimeters V being the voltage accelerating the electrons, in volts.

0 being the center of solenoid (sf and b the point where the yoke (h' vis located, the electric current i must vary, as a function of time t,in such a manner that the electrons remain focussed on oil layer Pduring all the scanning of the horizontal lines (ad) of E in thedirection of arrow f.

If ab is relatively large in comparison with aa' (Figure 3c), the anglebetween the perpendicular [212' on oil layer P and the electron pencilmay be considered as nearly constant and equal to (p ((p being the anglebetween bb' and the straight line joining point b to a point of abscissa(referred to point a) X /sE for example (E being the width of rectangleE and 0 the minimum angle be tween the electron pencil and oil layer PLet i be the intensity of the electric current in the winding of soleoid(sf corresponding to a perfect focus,- sing of the electrons on P whenthe electron spot is precisely at said point of abcissa X on scanningline aa':

If current i varies as a function of time t in accordance with thefollowing equation:

ly produced by, means of formation TF shown at the 1 i right of Figure3c: TF is a cathode ray tube having a rectilinear vertical cathode K,aWenhelt cylinder W, a pair 'of horizontally deflecting plates P, aslotted electrode SE, and a collecting electrode CE. Cylinder W controlsthe intensity of the flat electron beam produced by cathode K; plates Pare energized by the relaxation oscillation generated by oscillator O(Figure l), for the horizontal scanning (at constant velocity v ofrectangle E therefore the vertical electronic image of cathode K movesalong the slot of electrode SE in synchronism'v with said horizontalscanning of E The lines synchronizing pulses t (received from thedistant television transmitting station) are applied to cathode K andcylinder W of tube TB, in order to cut off the electron beam during therapidly decreasing part of' the waveform of the relaxation oscillationproduced by O (see, on Figure 3c, the lines representing, as functionsof time I, said relaxation oscillation and said lines synchronizingpulses t The slotted electrode SE (represented at the bottom of theright side of Figure 3c) is provided with a slot having a lowerhorizontal edge and an upper edge of a shape corresponding precisely tothe above formula:

d are tan with E: 198 millimeters and the maximum variation of the focallength F of focussing solenoid (sh) acting as a magnetic lens is:

AF=E cos 0 In case of Figure 3b, d=133 rnm., tan 0= 7i9 =0.67, 0:339degrees, cos 0:0.83 and AF=l98 0.83-,-164 millimeters.

In case of Figure 3d, d=163 rnm., tan 0= =0.82, 0=39.4 degrees. Cos9:0.77 and AF=l98 O.77=l52 millimeters.

In case of Figure 3 (1) If ri -=16, n =l2.8, n,=9.l4, then d=108 rnm.,tan B= i =0.54, 19:28.4 degrees, cos 0:0.88 and Ar =198 0.88=174millimeters.

(2) If n =8, n =6.4, n,=4.57, then d=217 millimeters, tan 0=" =1.09,19:47.4 degrees, cos 6:0.676 and AF=198 0.676=132.6 millimeters.

If distance ba (Figure 30), between the yoke and the oil layer along theshortest length of the electron pencil is of the order of 50centimeters, the abberations of the electron spot of the oil layer atboth ends of a scanning line can be tolerated.

Referring again to Figure 1, plates 11; are energized by a sine-wave A.sin w t (generated by oscillator 0 having a constant frequency and anamplitude modulated by modulator (md under the control of a weightedluminance signal obtained at the output of electronic mixer (mxl), asexplained hereafter, electric filter F suppressing the carrier and oneside-band; plates I1 are energized by a sine-Wave C =A .sin w tgenerated by oscillator 0 and frequency modulated by modulator (md asexplained hereafter; this wave (C ==A .sin cu l) controls the productionof elemental diifracting gratings on the surface of oil layer P insidethe various elemental squares of rectangle E corresponding to thevarious colored touches superimposed by objective LO on the detailedblack and white drawing produced by objective LC; on projection screen15?.

The frequency fi 2r of wave C =A .sin m varies (as a function of time I)by successive steps, under the control of a device (described hereafterand shown on Figure 1, or on Figure 2 or on Figure 2e, or on Figure 2g).Said frequency modulated wave (A sin to l is applied to the control gridg of a gated amplifier (tetrode lb), the gating grid g of which isenergized by the output C of hue decoding cathode ray tube Td." Thistube Td is itself controlled by the output voltage C of a phase detectorDP (represented schematically on Figure. 20); to said phase detector DPare applied simultaneously, on one side, the amplified voltage ofoscillator 0 (having same frequency and phase as the color burst sr, oras the oscillator generating the color subcarrier at the distanttransmitting station), and, on the other side, through amplitude limiter(la), the received chrominance signal (chr) the phase of whichcharacterizes the hue of the color to be reproduced; therefore thevoltage C obtained at the output of phase detector DP, proportional tothe cosine of the phase-shift between signals (chr) and (sr),characterizes also the color to be reproduced.

For the. step by step modulation of the frequency f of oscillator 0 anytype of telegraphic frequency modulator may be used. For example thestep-voltage ech (Fig. 1, having 3 successive values in each period) isapplied to the conveniently biased grids of triodes, the outputs ofwhich short-circuit (or insert) successively (without inertia) one ortwo parts of the inductance coil 1 (or of the capacitor 0) of theanti-resonant circuit (10) of an electronic tube having its grid andplate circuits coupled together, so that this tube oscillates with afrequency which varies step by step as a function of time; in thismanner, it is possible to produce frequency deviations which are greatby comparison with the basic frequency.

The number of lines n (per millimeter) of an elemental diffractinggrating R produced on oil layer P of cathode ray tube TC by theelectrons issued from cathode 0 is a function of the instantaneousfrequency of the frequency modulated wave (C =A sin w t) applied to theplates 11 which make horizontally vibrate the electron pencil producedby cathode 0 At each instant, this number of lines 12 must be such thatonly the monochromatic radiations having wave lengths close to a value(corresponding to the received chrominance signal (clzr), and,therefore, to the hue of the color to be reproduced) can go through thetransparent parts (2) of mask M in front of grating R in order toproduce, on projection screen EP, a luminous spot having the desiredcolor.

As an elemental diifracting grating is produced by an electron spot (onthe oil layer) having a width of 0.02 millimeter and a length of 0.1millimeter, it is possible to have a few elemental gratings in anelemental area (square of 1.5x 1.5 millimeter) within rectangle E of oillayer P (Figure l), which corresponds to the coarse colored picture tobe produced on projection screen EP; various combinations of gratings(giving blue, or green, or red light, respectively) within the sameelemental square of rectangle E may be considcred; two such combinationsare described hereafter, in way of examples only, being understood thatmany other combinations could be realized within the frame of thepresent invention.

In the first case considered hereafter, six gratings (having each aheight of 0.1 millimeter) are located inside said elemental square(height 1.5 millimeters) of rec: tangle E of oil layer P Said rectangleE is horizon- 13 tally scanned by the interlace process, each horizontalline being swept by the electrons during L Y 1-- second in the Americantelevision standards. In the case of Figure l (N.T.S.C. color televisionsystem), there are 133 elemental squares in rectangle E and thereforeeach elemental square is swept during a time or approximately /2microsecondJ If, on three successive lines of the same field (lines q,q+2, q+4) are produced successively (within a given elemental square ofE a grating R giving red light, a grating R giving green light, and agrating R giving blue light, and if the same process is applied to lines(q-i-l), (q+3) and (q+) of the following field, it is apparent that, onsaid six lines (q to 4+5), the color to be reproduced (for theconsidered elemental area of the scene scanned at the transmittingstation) will be obtained twice inside this elemental square ofrectangle E.

In the second case hereafter considered, (within a given elementalsquare of E a grating R for red and a grating R for green arealternately produced on two successive lines of the same field (lines qand q+2, for example), whereas gratings R5 for blue are produced on allthe lines of the field which follows (lines. (q-I-l), (q+3), etc.); acolor filter absorbing slightly the blue luminous radiations can, inthis case, be located in front of mirror M of Figure 1; said colorfilter is not shown on Figure l.

' As an elemental square of rectangle E is swept during a time 15 second,,=%=n,.2.1.10 hertz The values of the instantaneous frequency icorresponding to the creation'of blue, green or red lights on projectionscreen EP are therefore:

(1) In the case where:

(2) In the case where:

n =16, n =12.8 and n,=9.l4 f =33.6 megahertz f =26.88 megahertz In anEidophor projector, the voltage to be applied to the auxiliarydeflecting plates (h or I1 on Figure 1) is of the order of 1 volt only;oscillators O and 0 (Figure 1) are therefore of the low power, highfrequency type.

In the first case (considered hereabove), the frequency f, of oscillator0 must have the instantaneous value 1, during a 1' second (duration ofone scanning line in the American television standards), then, the value1, during the following period r, then the value f during the nextperiod T, and soon. For achieving that, use can be made of generator GR(Figure 1) producing square waves having a period equal to 31- (saidgenerator GR being synchronized by.the received line synchronizingpulses t, at scanning lines fre: quency).

CD is a diiferentiating circuit (the word difierentiating havingitsrnathematical meaning), producing apositive pip for the initial riseof I each pulse, and, a negative pip for the final transient part ofsaid pulse. These pips trigger two multivibrators (MV, MV') producingtwo similar square-wave outputs, degrees out of phase, one pulse (ofeach cycle) having a duration 2-r, whereas the pulse of the other has aduration of 1. After passing through a clipper in each channel (dc, dc),these two pulse signals are mixed in electronic mixer MX, to achieve a 3step-voltage wave-form with a step duration of '7". After amplificationby amplifier AM, th desired 3 step-voltage ech (having three successivevalues in each period 37) is obtained, said values cor-, responding totheratios between the desired instantaneous frequencies for the wave C=A sin 0: 1, that is to say: in f f This 3 step-voltage (ech) modulatesthe frequency of the sine-wave generated by oscillator 0 by means of thefrequency modulator (mdl) of telegraphic type.

V The frequency modulated wave (C =A sin w t) is ap plied to the controlgrid g of gated amplifier lb, the gating grid g of which is controlledby the output of hue decoding tube Ta', and is negatively biased bybattery B.

Decoding tube Td (Figure 1) has a small cathode K, horizontallydeflecting plates H (energized by phase detector DP), verticallydeflecting plates V (energized by the 3-step voltage ech of period 31'),a decoding.elec-' trode ED (represented on Figure 2d, and having 3 slitsR, V, B), and a collecting electrode EC behind said slits. At eachinstant, the electronic image of cathode K is (under the control of 3step-voltage ech) located at the level of one of said 3 slits ofdecoding electrode ED, at a point determined by the voltage C (producedat the output of phase detector DP and applied to dc:v fleeting platesH). Said electronic image is, in case of Figure l, on slit R(corresponding to red primary color) during a time 'r, then,'on slit V(corresponding to green primary color) during the following period 7-,then, on slit B (corresponding to blue primary color) during thefollowing period 7", and so on, under the'control of 3 step-voltage echapplied to plates V of tube Td.

The voltage C =2E cos (oc/ as explained hereafter, characterizes the hueof the color to be reproduced, and is therefore called hereafter huesignal; acting on plates H of tube Td, said hue signal positions, ateach instant, the electronic image of cathode K on a particular verticalline of deco-ding electrode ED cutting one, or two, or three slits (Rred, V green, B blue) if one, or

two, or three primary colors are necessary for the reproproduction ofthe color on the corresponding part of jection screen EP. If, at a giveninstant, the electronic image of cathode K is on a solid part ofdecoding electrode ED, no electron can reach collecting electrode EC,and the output I voltage C of tube Td is unable to equalize (or exceed)sawtooth Wave of oscillator Oh (acting on coil h' moves the electronpencil of tube TC the oil layer P has no deformation (no grating) atthis place; no light is produced by tube T C on the corresponding pointof projectiOn, screen ,EP. 7

If, on the contrary, at a given instant, the electronic image of cathodeK is, for example, on a point of slit V of electrode ED, collectingelectrode EC receives electrons, and (at the output of tube Td) a signalC is produced with an intensity exceeding the voltage of battery Bbiasing gating electrode g of tube lb; the frequency modulated wave (C=A sin c 2) applied to control grid g of lb is amplified, and reachesplates hf of tube TC precisely, at this instant, the instantaneousfrequency n (fll 27r of Q; has the value f necessary for producing, onoil layer P in tube TC an elemental difiracting grating R having n,lines per millimeter and giving green light (through mask M andobjective lens L0 on the appropriate point of projection screen EP,because rectangles E and E of oil layers P and P (Figure 1) arehomothetic, and are scanned in perfect synchronism, with the samerelaxation oscillators O and 0 Instead of the frequency modulator mdlshown at the bottom of the left of Figure 1, use can be. made. of thedevice shown on the appended Figure 2f. G 6,, G represent oscillatorsgenerating for example sinewaves having respectively the frequencies f f1, proportional to the numbers (n 11 11,) of lines per millimeter of theelemental diffracting grating R R R these waves are applied respectivelyto the control grids (g g g,) of amplifiers a a a the gating grids ofwhich are g' g' g,-. D is the arrangement of Figure 1 generating athree-step voltage (ech) having a period 37' ('1' being the duration ofone scanning line); D is synchronized by the lines synchronizing pulsest coming from the distant television transmitting station.

(com) is a 3 contact beam switching tube; for example, as shown onFigure 2f, (com) is a cathode ray tube having a cathode c, verticallydeflecting plates V, an electrode E provided with 3 holes above eachother and behind which are located three collecting electrodes e e econnected respectively to three output resistors r r r;;. The voltagesproduced across said resistors are applied to the gating grids g g' g ofamplifiers a a a respectively. Td is the hue decoding tube of Figure 1,and lb is its associated tetrode acting as gated amplifier, with acontrol grid g and a gating grid g negatively biased by battery B andcontrolled by signal C produced by tube Td. The vertically deflectingplates v of tube (com) and V of tube Td are both energized by said 3step voltage (ech). The plates of amplifiers a a 11,- are connected toelectronic mixer M which feeds the control grid g of tetrode lb.

When the electronic image of cathode c of tube (com) is successively infront of collecting electrodes e e e (during three successive scanninglines of duration '1'), the electronic image of cathode K of tube Td isprecisely at the level of slits R (red), V (green) and B (blue) ofdecoding electrode ED of tube Td, successively; and, precisely, at thesame instants, the voltages across resistors r r r (acting on gatinggrids g',, g,,, g' of amplifiers a a a unblock successively saidamplifiers; therefore control grid g of tetrode lb receives successivelythe frequency modulated sine wave C =A sin w t (to be applied todeflecting plates h; of tube TC Figure l) with the successiveinstantaneous frequencies (f f f which are necessary for creating theelemental diifracting gratings R R R on rectangle E of oil layer P ofsaid tube TC In the second case considered above, the instantaneousfrequency i of Wave A sin. of must have the value 1, during a period 1'second on during two successive lines of the first field; during all thesecond field (in interlace scanning), the frequency f must keep the samevalue f In this case, instead of the device represented at the bottom(on the left) of Figure l, for generating the frequency modulated wave C='A -sin w t, use is made of the device shown on Figure 2e. 0; is anoscillator generating a wave of constant frequency f O is an oscillatorgenerating a wave of frequency i having the value f during a period 1',when all its inductance coil 1 (or all its capacitor c) is inserted inthe anti-resonant circuit, and having the value f during the followingperiod 7- when an appropriate part of said inductance coil 1 (or of saidcapacitor c) is short-circuited, the freq y (in) being The electronicdevice md (Figure 2e), synchronized by the received line synchronizingpulses t operates this short-circuiting of part of coil 1 (or part ofcapacitor c); the electronic switch (basc), synchronized by the receivedfield synchronizing signals t connects alternately, in two successivefields, oscillator 0 and oscillator 0' to the control grid g; of gatedamplifier lb of Figure 1.

At the same time, the vertically deflecting plates V of tube Td(Figure 1) are energized by the device shown on Figure 2e: GR is agenerator of a square-wave of period 27 (one pulse 1- wide, everyperiod), synchronized by the received lines synchronizing pulses t andbringing the electronic image of cathode K of tube Td successively atthe level of slit R and at the level of slit V of decoding electrode EDof tube Td during two successive scanning lines of one field, whenelectronic switch (basc) is on its left hand side contact; during allthe following field, electronic switch (basc)-synchronized by thereceived field synchronizing signals t is on its right hand contact andconnects plates V to a battery P producing (across plates V) a voltagebringing the electronic image of said cathode K, at the level of slit Bof said electrode ED.

Instead of the device shown on- Figure 22, use can be made of the deviceshown on Figure 2g. 1- being the duration of one scanning line and T theduration of one field, use is then made of two multivibrators: (mvl),producing one square pulse 1- wide every 2 '7' seconds, and (mvi),producing one square pulse T wide every 2T seconds. These twomultivibrators are respectively synchronized by the received linessynchronizing pulses t and by the received field synchronizing signals 1(mvl) controls directly the gating grid g, of amplifier a fed by G,,which generates a sine-wave of frequency f (mvl) controls indirectly(through inverting triode i the gating grid g of amplifier a fed by Gwhich generates a sine-wave of frequency f,. The output voltages ofamplifiers a and a are applied to electronic mixer m (mvi) controlsdirectly the gating grid g' of amplifier a which is fed by electronicmixer m mvi controls indirectly (through inverting triode i the gatinggrid g' of amplifier a which is fed by 6,, generating a sinewave offrequency f The: output voltages of amplifiers a and a are applied toelectronic mixer m which energizes the control grid g of tetrode lb,whereas, the: gating grid g; of said tetrode lb is, negatively biased bybattery B and is also submitted to the control of signal C produced atthe output of hue decoding tube Td. The horizontally deflecting plates,H of Td are energized by hue signal C whereas the vertically deflectingplates V are energized by electronic mixer. m to the input of which areapplied; 1) through amplifier a the. wave produced by (every 21 second:

(mvl), and (2) through amplifier a a positive DC. voltage due to batteryP. The gating grid g of amplifier a is directly controlled by (mvi), andthe gating grid g' of amplifier a is indirectly controlled (throughinverting triode i' by (mvi). During the field when a is unblocked,plates V of tube Td position the electronic image of cathode Ksuccessively at the level of slit R and at the level of slit V of EDduring two successive scanning lines; during the following field, a isunblocked and said electronic image of K is positioned at the level ofslit B of ED. I

Several modifications may be done in the electronic devices (describedhereabove) for producing awave of varying periodicity in order to createelemental diffracting gratings on oil layer P of tube TC (Figure 1). Forexample, instead of applying to horizontally deflecting plates h of tubeTC a sine-wave of variable frequency (A .sin a t), use can be made ofperiodic wave-shapes other than a sinusoid; for example, oscillators Oand 0' (Figure 2e), or devices G G G (Figure 2] or Figure 2g) cangenerate saw-tooth waves, or rectangular waves, having appropriatefundamental frequencies; if a rectangular wave-form is used, the ratiobetween the duration of the rectangular pulse and the time intervalbetween 2 consecutive pulses should have an appropriate value.

As the intensity (but not the positions) of the diffraction spectradepends on the ratio between the width of a line and the distancebetween two consecutive lines of the diifracting grating, it is possibleto use, as generators G G Gr of periodic waves of respectiveperiodicities f f (Figure 2f, or Figure 2g), devices generatingperiodical rectangular waves, having (in each period) a pulse, theduration of which is function of the lowfrequency part I of the receivedluminance signal, but only when the elemental area of the scene (beingscanned at the transmitting station) to be reproduced on the projectionscreen at the receiving station has a uniform, very saturated color,with brightness variations from one point to the other. 7

Such a device comprises: (1) a multivibrator MV generating a rectangularwave of desired periodicity, (2) a modulator MA, for modulating theamplitude of the rectangular pulse within the successive periods, (3) aconverter (CAD) for changing the pulse-amplitudemodulation into apulse-duration-modulation, and (4) an amplifier A to the control grid ofwhich is applied said low-frequency part I of the luminance spectrum,whereas its gating grid is negatively biased by a battery, and is alsosubmitted to the action of saturation signal S (which is proportional tothe degree of saturation of the color to be reproduced).

The output voltages of amplifier A and of multivibrator MV are appliedto amplitude modulator MA; but A is blocked except when a very saturatedcolor must be reproduced, so that saturationsignal S then exceeds thevalue of the negative bias of the gating grid.

Only in such a case, amplifier A is active, and applies with the desiredamplitudes) the low-frequency part Z of the received luminance signal toamplitude-modulator MA, for modulating the amplitudes of the successiverectangular pulses generated by, multivibrator MV; converter CAD changessaid pulse-amplitude-modulation into pulse-duration-modulation; so isobtained, at the output of converter CAD, a periodical wave having thedesired periodicity (f f or f,), and having (in each period) a pulse,the duration of which is a function of the luminance to be reproduced;this periodical wave provides, on oil layer P of tube TC (Figure 1),successive diifracting gratings having all the same number of lines permillimeter,,but different ratios between the width of a line and thedistance between 2 successive lines; said gratings produce successivediffraction spectra having different luminous intensities, in accordancewith the time variations of the received luminance energy. Therefore, on

projection screen EP (Figure 1), colored touches of the same verysaturated color, but of different brightness are successively produced.

The two Eidophor projectors TC; and TC of Figure 1 cooperate as followsunder the control of the received composite video-signal V restored, atthe receiving station, after the video-detector DV. SVS is thesynchrovideo-separator (amplitude filter), which separates the linesynchronizing pulses t (controlling the sawtooth wave generator Oh), thefield synchronizing signals t (controlling the sawtooth wave generatorOv), and the video-signal carrying the luminance and chrominanceinformations and having the spectrum represented on Figure 2a, in caseof the N.T.S.C. color television system; after amplification byamplifier A (band width B Figure 2a), the video-signal spectrum isdivided by electronic frequency filters in the following manner:

Filter F (bandwidth B Figure 2a) separates the part I" of the luminanceconcerning the principal details of the drawing of the scene beingscanned at the distant transmitting station;

Filter F' (bandwidth B' Figure 2a) separates the chrominance (chr),(modulated color subcarrier), with negligible components of luminance;

Filter F (bandwidth B equal to B Figure 2a) separates the part I of theluminance containing the greatest part of the luminance energy.

A is an amplifier having a very narrow frequency band (centered on thecolor subcarrier frequency), and having a gating grid g controlled bythe received line synchronizing pulses t A separates (at the beginningof each scanning line) the color burst sr (color reference signal) madeof a few periods of the unmodulated color subcarrier. I

O is a local oscillator generating a sine-wave at the color subcarrierfrequency; the phase and frequency of said wave are maintained inperfect synchronism with the oscillator generating the color subcarrierat the. transmitting station in the following classical manner: the

wave produced by O and the received color burst sr are.

simultaneously applied to phase detectordp, the output of which (throughcircuit ct, of appropriate time constant) controls the bias of areactance tube associated with oscillator 0, so that any accidentalphase-shift between Dominant wavelength I. (hue) of the color to bereproduced, exnressed in mieronsXl0- Difference of phase (a-fl) betweenthe chrominance signal (chr) and the color burst (8)); relative valuesin degrees Color to be reproduced 0 700. 10361=42 complementary to 510.180-(347283)=116 420. 180 .495. l+42=222 510. l80+116=296 575.

tr to the plates of diodes V V the amplitude E being much larger thanamplitude E because of the action of amplifier a, and E beingpractically constant because of the action of amplitude limiter la. Atthe output of phase detector DP (Figures 2c and l), a wave C =2E .cos(Gt-B) is obtained: it is the hue signal characterizing the hue of thecolor to be reproduced, and applied to the horizontally deflectingplates H of hue decoding cathode ray tube Td.

In case of a purely black (or purely white) part of the scene beingscanned at the transmitting station, the color subcarrier is no moremodulated at said station and reaches the receiving station with thesame phase as the color burst sr. Therefore. the hue signal [C =2E .cos(a 3)] is zero, and plates. H position the electronic image of cathode Kof tube Td on the solid part (on the, left) of decoding electrode ED(Figure 1 and Figure 2d). Then signal C at the output of tube Td, isunable to overcome thebias B- of the gating grid g of tube lb, and nosignal (C =A .sin w t) reaches the auxiliary deflecting plates I1 ofEidophor projector TC no deformation is produced in rectangle E of oillayer P and no colored light is thrown by projector TC on projectionscreen EP, on which remains only the black and White drawing of thescene being scanned at the transmitting station.

Referring again. to Figure l, the part 1 (band 13 of the luminancespectrum is, at the output of filter F applied to the control grid ofpentodeL acting as luminance weighting device; after amplitude detectorDA, the amplitude of the received chrominance signal chr (colorsubcarn'er, amplitude modulated by the degree of saturation of the colorat the transmitting station) constitutes the saturation signal Sproportional to the degree of saturation of the color to be reproducedat the receiving station; said saturation signal S provides (throughrheostat r, r), to the control grid of pentode L, a bias such that thegain of said pentode varies in inverse proportionality to the degree ofsaturation of the color to be reproduced on projection screen EP.Consequently the voltage at the output of pentode L is greater, thesmaller S (or said degree of saturation) is.

Electronic mixer (mxl) mixes said output voltage 1' with part I of theluminance spectrum. (band B Fig ure 2a) carrying the details ofthedrawing of the scene being scanned at the transmitting station. Theweighted. luminance signal so. obtained at the output of mixer (mxl)modulates the amplitude of the wave (A .sin w t) generated by oscillatorthrough amplitude modulator (ma' After filter F (which suppressesthe.carrier and one side-band), the singlesideband-amplitude-modulatedwave (A sin w t) energizes plates I1 ofEidophor projector TC which, in the classical manner, provides, afterreflection on mirror M the desired black and white drawing on screen EP;the right proportions between the white light produced by TC and thecolored light produced by T C are secured by the appropriate adjustmentof rheostat r, r.

As mask M (Figure 1) associated with projector TC; cuts off the centralwhite image I of source S but only of the spectra (s and s,) on bothsides of said image I (see Figure 3a), there remains a small amount ofwhite light in the colored touches brought by TC; onto screen EP;account of this fact is taken when adjusting the rheostat r, r whichprovides the bias of the control grid of pentode L. Said rheostat r, rmust be adjusted also in such a manner that electric voltage l' (at theoutput of pentode L) be zero when saturation signal S is maximum,because the color to be reproduced then is very saturated.

When a relatively large part of the scene being scanned at the distanttransmitting station has. a uniformly very saturated color, part I ofthe luminance spectrum (band B Figure 2a) still acts (through mixer mxl,oscillator O and amplitude modulator Indon plates I1 of projector TC(although 1' is then equal to zero); while the brightness of the coloredtouch produced by projector T C remains constant (it the amplitude A ofthe frequency modulated wave (C =A .sin w t) applied to plates I1remains constant), part I" of the luminance spectrum produces saturationvariations which give the illusion of brightness variations for thesmalldetails. of said part of said scene.

Figure 1c illustrates the case when it is possible to have a largetransparent plate PL with an oil layer P inside one single Eidophorprojector TC (replacing the tubes T C and TC of Figure 1): two pencilsof electrons scan respectively, in perfect synchronism, the homotheticrectangles 13 ,15 on the surface of said oil layer P, plate PL rotatingslowly in the direction of arrow 1 within tube TC. R is a small oilcontainer below tube TC, although it is shown, on Figure 10, as atransversal cut brought in the plane of plate PL. The oil is deliveredunder pressure to plate PL (from container R, through pipes 12 p and oilfilters F F by means of, delivering bars ba 11:1 having slots close tothe surface of PL, and lying in a radial direction. As the plate PLrotates, the oil is trans ported. to similarly arranged smoothing barsbe be Whose distance to plate PL is such that the thickness of the oillayer is of. the order of 0.1 millimeter in the useful parts, whererectangles E B are bombarded by electrons.

Protecting bars bp bp protect said useful parts against any disturbancedue to the liquid delivered in a direction opposite to arrow 1 (which isthe direction of rotation of PL).

On the other side of said protecting bars, said liquid delivered in adirection opposite to arrow 1 pushes away the oil already bombarded, andhence partially polymerised by the electron beams. The protective bars(bp bp are maintained at a low temperature in order to cool said alreadybombarded oil, which then (together with the newly delivered excess oil)flows into container R, under plate PL.

P is a recirculating pump (inside container R); the viscous oil entersthe chamber where the slowly moving smooth rotor of P transports italong a narrow slit to a barrier (nearly touching the rotor); the oil isso forced under pressure into delivering bars ba ba -and any undesirabledisturbance of the oil surface is so avoided.

Figure 1d illustrates the operation of delivering bar ba smoothing barbe protecting bar bp and also the evacuation of the already. bombardedoil towards container R, under plate PL, which rotates in the directionof arrow 1; the oil is represented by small dots on said Figure 1b. Thenumerical values quoted in the above description must be considered onlyas orders of magnitude.

The above description concerns the application of the invention to theAmerican N.T.S.C. color television system; but this invention can beapplied, just as well, to any compatible color television system basedon any kind of coding of the luminance and the chrominance.

Figure 4 (for example). shows the color triangle divided in sectorscorresponding to the various chromaticities that the human eye caneasily discriminate from each other; on said triangle (so divided) isbased a color television system in which the color subcarrier ismodulated only inamplitude by a chrominance signal," which is a voltage.proportional to the number of the sector representing the chromaticityto be reproduced at the receiving station; this chrominance signal"therefore carries informations concerning both the hue and the degree ofsaturation of said chromaticity to be reproduced. In this case, thephase detector DP of Figure l is not used any more, and the amplitudedetector DA (Figure 4a.) feeds directly the horizontally deflectingplates H,,H of two decoding cathode ray tubes Ta, Td', decodingrespectively the saturation signal S, and the hue signal C correspondingto the desired chromaticity.

The saturation decoding cathode ray tube Td contains 21 V 2: Verticalrectilinear'cathode and a decoding electrode ED provided with a slithaving one rectilinear edge and one sinuous edge, because signal C(produced by amplitude detector DA energized by the received modulatedcolor subcarrier at the output of filter F' applied to plates H, isproportional to the various numbers of the sectors of the triangle ofFigure 4, whereas the degrees of saturation (of the chromaticitiesrepresented respectively by said sectors) vary alternately from a lowvalue (for a central sector) to a high value (for a peripheric sector)when the increasing order of sector numbers is followed. The huedecoding cathode ray tube Td (Figure 4a) operates like the same tube Tdon Figure 1.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the stand-point of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention,and, therefore, such adaptations should, and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. Color television receiving station of the type in which the receivedluminance signal controls the production (on a projection screen) of adetailed black and white drawing of the scene being scanned at thedistant transmit ting station, while the received chrominance signalcontrols the production of a relatively coarse colored picture of saidscene superimposed'on said black and white drawing, comprising incombination: means for separating from each other said receivedluminance signal, said received chrominance signal, the color referencesignal or color burst received at the beginning of each scanning line,the received lines synchronizing pulses, and the received fieldssynchronizing signals, means for extracting (from said chrominancesignal) a so-called hue signal characterizing the hue of the color to bereproduced, and a so-called saturation signal proportional to the degreeof saturation of said color to be reproduced, a luminance weightingdevice controlled by said received luminance signal and by saidsaturation signal, for producing a socalled weighted luminance signal, afirst oscillator, an electronic amplitude modulator associated with saidfirst oscillator for producing a wave of constant frequency, whoseamplitude is modulated by said weighted luminance signal, a devicegenerating a wave of varying periodicity, a gated amplifier having itscontrol grid energized by said wave of varying periodicity and itsgating grid negatively biased, said hue signal being applied to saidgating grid for unblocking said amplifier when said hue signal overcomessaid negative bias, two cathode ray tubes having each a transparentrotating plate with an oil layer, the face of said plate in contact withthe oil being electroconductive and raised to a high positive potentialreferred to the cathode, two relaxation oscillators respectivelycontrolled by said receiving lines synchronizing pulses and by saidreceived fields synchronizing signals, deflecting coils acting on theelectron pencils of said tubes and energized by the saw-tooth wavesgenerated respectively by said relaxation oscillators, whereby twohomothetic rectangles of the oil layers of said tubes are scanned, inperfect synchronism, horizontally and vertically with const-antvelocities, power sources of white light illuminating, at normalincidence, through said rotating transparent plates, said homotheticrectangles of said oil layers, deflecting plates energized by said wavehaving its amplitude modulated by said weighted luminance signal, forproducing a vibration of constant frequency superimposed on saidconstant velocity horizontal sweeping, whereby deformations are producedon the surface of the oil layer of the first of said cathode ray tubes,two optically conjugated bar systems through which can pass only thewhite light diffracted by the deformations of said oil 22 layer, a firstobjective imaging said deformations of said oil layer onto saidprojection screen, for producing said detailed black and white drawingof the scene scanned at the distant transmitting station, deflectingplates energized by said wave of varying periodicity, for producing avibration of variable periodicity superimposed on said constant velocityhorizontal sweeping, whereby deformations are produced on the surface ofthe oil layer of the second of said cathode ray tubes, a mask made ofopaque parts separated by transparent parts through which can pass onlythe desired colored light diffracted by the deformations of said oillayer, a second objective imaging said deformations of said oil layeronto said projection screen for adding colored touches to said detaileddrawing, whereby said scene, being scanned at the distant transmittingstation, is reproduced in colors on said projection screen.

-2. Color television receiving station in accordance with claim 1 inwhich a network of elemental lenses is associated with said mask, saidelemental lenses corresponding to the various elemental squares of therectangle of the oil layer being scanned by said electron pencil whichvibrates under the control of said wave of varying periodicity.

3. Color television receiving station in accordance with claim 2, inwhich said mask is located on the plane containing the focal points ofall said elemental lenses.

4. Color television receiving station in accordance with claim 2comprising: a network of elemental lenses corresponding to the variouselemental squares of said rectangle of oil layer scanned by saidelectron pencil which vibrates under the control of said Wave of varyingperiodicity, a mask made of opaque parts separated by transparent parts,and located immediately below said network of elemental lenses, a barsystem for making perfectly parallel the rays of white lightilluminating said rectangle of oil layer, and a screen provided withsmall holes, and located in the plane'containing the focal points ofsaid elemental lenses, for suppressing any light except the desiredcolored lights.-

' 5. Color television receiving station in accordance with claim 1comprising: a bar system through which pass the white luminous raysilluminating said rectangle of the oil layer scanned by said electronpencil which vibrates under the control of said wave of varyingperiodicity, and a mask, located on the other side of said oil layer,and having opaque parts exactly above the slits of said bar system, saidopaque parts being separated by transparent parts through which passonly the desired colored lights.

6. Color television receiving station in accordance with claim 1 inwhich said device generating said wave of varying periodicity comprises:an oscillator generating a sine-wave, a frequency modulator oftelegraphic type acting on the anti-resonant circuit of said oscillator,and a 3-step voltage generator controlling said frequency modulator andsynchronized by said received lines synchronizing pulses.

7. Color television receiving station in accordance with claim 1 inwhich said device generating said wave of varying periodicity comprises:a first oscillator generating a sine-wave, a frequency modulator oftelegraphic type synchronised by the received lines synchronizing pulsesand acting upon the anti-resonant circuit of said first oscillator, asecond oscillator generating another sine-wave, and an electronicswitch, synchronized by the received fields synchronizing signals, forsubstituting said second oscillator to said first oscillator every twofields.

8. Color television receiving station in accordance with claim 1 inwhich said device generating said wave of varying periodicity comprises:three oscillators generating three sine-waves of fixed frequencies,three gated amplifiers fed by said oscillators, an electronic switchopening successively the gates of said amplifiers, and a device,synchronized by the received lines synchronizing pulses, generating a3-step voltage controlling said electronic switch.

9. Color television receiving station in accordancewith claim 1 in whichsaid device generating said wave of varying periodicity comprises: threeoscillators generating three sine-waves of fixed frequencies, gatedamplifiers and electronic mixers associated with said oscillators, andtwo multivibrators acting on the gating grids of said amplifiers, andrespectively synchronized by the received lines synchronizing pulses andthe received fields syrichronizing signals.

10. Color television receiving station in accordance with claim 1, inwhich the voltage of varying periodicity, applied to the auxiliaryhorizontally deflecting plates ajcting on the electron pencil of thetube producing colofr'e'd' touches on said projection screen, has asaw-tooth waveform, having a period corresponding successively to thenumbers of lines (per millimeter) of the elemental diffracting gratingsto be produced on the oil' layer of said tube.

11. Color television receiving station in accordance with claim 1, inwhich the voltage of varying periodicity, applied to the auxiliaryhorizontally deflecting plates acting on the electron pencil of the tubeproducing colored touches on said projection screen, has a rectangularwaveform of appropriate ratio (between the duration of the rectangularpulse and the time interval between two consecutive pulses), and has afundamental period corresponding successively to the numbers of lines(per millimeter) of the elemental diffracting gratings to be produced onthe oil layer of said tube..

12. Color television receiving station in accordance with claim 11, inwhich the devices acting on the electron pencil of the tube producingcolored touches on said projection screen comprise: a multivibratorgenerating a rectangular wave of a periodicity corresponding to aprimary component of the hue of the color to be reproduced, a modulatorfor modulating the amplitude of the rectangular pulse within thesuccessive periods of said wave, a converter ofpulse-amplitude-modulation into pulse-duration-modulation, and a gatedamplifier, the control grid of which is energized by the low-frequencypart of said received luminance signal, whereas the gating grid isnegatively biased by a battery, and is also submitted to the action ofsaid saturation signalproportional to the degree of saturation of saidcolor to be reproduced, the output voltages of said amplifier and ofsaid multivibrator being applied to said amplitude modulator,

24 whereby, at the output of said converter, but only during thereproduction of very saturated colors, is obtained a periodical wavehaving a periodicity corresponding to said primary component of color tobe reproduced, but having, in each period, a pulse of a durationfunction of the luminance to be reproduced.

13. Color television receiving station in accordance with claim 1, inwhich a single cathode ray tube with two electron guns replaces the twotubes recited in claim 1, said single tube comprising: a rotatingtransparent plate with an oil layer, two homothetic rectangles of whichare scanned, in perfect synchronism, by the electron pencils issued fromsaid electron guns, an oil container located under said transparentplate, a rotating pump inside said container, two deliveringbars fed inoil by said pump, for delivering oil to said transparent plate, twosmoothing bars, for giving a small uniform thickness to the useful partsof said oil layer where said homothetic rectangles are located, twoprotecting bars, for protecting said useful parts against anydisturbance due to the oil delivered in a direction opposite to therotation of said transparent plate, and a device for maintaining saidprotecting bars at a low temperature, in order to cool the oil alreadybombarded by said electron pencils. i

14. Color television receiving station in accordance with claim 1, inwhich the devices for focusing theelectrons (of the electron pencils ofsaid' tubes producing on said projection screen the pictures of thescene being scanned at the transmitting station) upon the oil layers ofsaid tubes, comprise: a solenoid acting as a magnetic lens on saidelectrons, a cathode ray tube provided with a rectilinear verticalcathode, a Wenhelt cylinder, a slotted electrode, a collecting electrodebehind said slotted electrode, and a pair of horizontally deflectingplates, energized by said relaxation oscillator which produces theconstant velocity horizontal scanning of said oil layers, and anamplifier, energized by the output voltage of said cathode ray tube, forfeeding the winding of said solenoid, said received lines synchronizingpulses being applied to said cathode andto said Wenhelt cylinder of saidcathode ray tube.

References Cited inthe file of this patent UNITED STATES PATENTS

